The long-term goal of this research is to elucidate the cell biological events which control the development of form and of molecular compartmentation in nerve cells. The compartmentation of neurons, as exemplified by the structural and functional differences between axons and dendrites, forms the anatomical basis for neuronal function. Many developmental neural disorders disrupt axonal and dendritic growth and injury to the adult nervous system frequently causes pathological alterations in neuronal compartmentation. This proposal focuses on three issues: the establishment of cell polarity, dendritic development and the determination of dendritic form, and the organization of neuronal microtubules that underlies compartmentation and dendritic growth. Nerve cell cultures prepared from the rat hippocampus will be used for this work because they permit controlled alteration of the cellular environment during development and allow direct observation and experimental manipulation of living cells. The first portion of this proposal concerns the determination of dendritic form. A statistical profile of the form of neurons in culture will be developed, then used to quantitatively assess how innervation modifies dendritic development. Further experiments will elucidate the role of cell contact and of functional activity in mediating the influence of innervation on dendritic growth. In the second portion of this proposal the establishment of axonal and dendritic domains and the growth of dendrites will be studied in living cells by time-lapse video recording in combination with electron microscopy. These observations will focus on the ultrastructural reorganization that accompanies the establishment of compartmentation, on the mode of dendritic branching and its contribution to dendritic form, and on the activity and ultrastructure of dendritic growth cones. The final portion of this proposal concerns the organization of the cytoskeleton as it relates to the establishment of compartmentation and dendritic growth. In order to trace the transport and assembly of cytoskeletal proteins within living cells, fluorescently labeled tubulin and MAP2 will be microinjected into single hippocampal neurons and their distribution will be followed by fluorescent microscopy.